U.S. patent application number 17/675896 was filed with the patent office on 2022-06-02 for multi-user communication in a multi-bss environment of an 802.11ax network.
The applicant listed for this patent is CANON KABUSHIKI KAISHA. Invention is credited to Stephane BARON, Patrice NEZOU, Julien SEVIN, Pascal VIGER.
Application Number | 20220174742 17/675896 |
Document ID | / |
Family ID | 1000006149761 |
Filed Date | 2022-06-02 |
United States Patent
Application |
20220174742 |
Kind Code |
A1 |
SEVIN; Julien ; et
al. |
June 2, 2022 |
MULTI-USER COMMUNICATION IN A MULTI-BSS ENVIRONMENT OF AN 802.11AX
NETWORK
Abstract
The invention provides multi-user communication in a MU Uplink
transmission opportunity in case of a multi-BSS environment of a
wireless network. Resource units with AID=0 or 2045 are available
for stations to transmit data to addressee virtual access points
(VAPs) other than the VAP having initiated the TXOP. The initiating
VAP receiving frames from the resources forwards them to the
appropriate addressee VAPs within the same physical AP. Responses
may be provided by the addressee VAPs directly to the stations or
via the initiating VAP or the representative VAP. This approach
increases the opportunities for the stations to access the medium
in case of multiple BSSs. Better usage of the MU Uplink OFDMA
transmission is also made.
Inventors: |
SEVIN; Julien; (SAINT AUBIN
DU CORMIER, FR) ; VIGER; Pascal; (JANZE, FR) ;
NEZOU; Patrice; (LIFFRE, FR) ; BARON; Stephane;
(LE RHEU, FR) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
CANON KABUSHIKI KAISHA |
Tokyo |
|
JP |
|
|
Family ID: |
1000006149761 |
Appl. No.: |
17/675896 |
Filed: |
February 18, 2022 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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16610406 |
Nov 1, 2019 |
11284435 |
|
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PCT/EP2018/060989 |
Apr 27, 2018 |
|
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17675896 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W 84/12 20130101;
H04L 5/001 20130101; H04W 74/006 20130101; H04W 74/0816 20130101;
H04L 5/0037 20130101 |
International
Class: |
H04W 74/08 20060101
H04W074/08; H04L 5/00 20060101 H04L005/00; H04W 74/00 20060101
H04W074/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 3, 2017 |
GB |
1707062.4 |
Claims
1. A wireless communication method in a wireless network comprising
a first access point and a first group of stations, the first
access point managing the first group of stations, the method
comprising following steps, at a transmitting station in the first
group of stations willing to transmit data to a second access point
managing a second group of stations: receiving a trigger frame from
the first access point, the trigger frame reserving a transmission
opportunity on at least one communication channel of the wireless
network, the transmission opportunity including resource units that
form the communication channel and that at least one of the first
group of stations can access to transmit data during the reserved
transmission opportunity; and accessing one of the resource units
during the transmission opportunity and transmitting data intended
to the second access point, over the accessed resource unit to the
first access point.
2. A wireless communication method in a wireless network comprising
a first access point and a first group of stations, the first
access point managing the first group of stations, the method
comprising following steps, at the first access point: sending a
trigger frame to reserve a transmission opportunity on at least one
communication channel of the wireless network, the transmission
opportunity including resource units that form the communication
channel and that at least one of the first group of stations can
access to transmit data during the reserved transmission
opportunity; in response to the trigger frame, receiving, over one
of the resource units during the reserved transmission opportunity,
data from a transmitting station in the first group of stations and
addressed to a second access point managing a second group of
stations; and forwarding the received data to the second access
point.
3. The method of claim 1, wherein any station registering with the
first access point is associated with a unique association
identifier used by the first access point to assign, to the
station, a resource unit in a transmission opportunity granted to
the first access point, and the resource unit conveying the data of
the transmitting station is assigned to an association identifier
not associated with a specific station.
4. The method of claim 3, wherein the association identifier not
associated with a specific station takes a first AID value to
signal a resource unit in which any station already registered with
the first access point can transmit data.
5. The method of claim 4, wherein the first AID value equals 0.
6. The method of claim 1, wherein the transmitted data include a
data frame intended to the second access point.
7. The method of claim 3, wherein the association identifier not
associated with a specific station takes a second AID value to
signal a resource unit in which a station not yet registered with
the first access points can transmit data.
8. The method of claim 7, wherein the second AID value equals
2045.
9. The method of claim 1, wherein the transmitted data include a
management frame intended to the second access point within a
procedure of associating the transmitting station with the second
access point.
10. The method of claim 1, wherein the resource unit conveying the
data of the transmitting station is a random resource unit to which
stations randomly access using contention-based access.
11. The method of claim 1, wherein the data include a frame header
in which at least one address field is set to a basic service set
identification, BSSID, uniquely identifying the second group of
stations.
12. The method of claim 11 further comprising, at the first access
point, determining whether a frame header of the received data
includes an address field set to the BSSID uniquely identifying the
second group of stations, and forwarding the received data in case
of positive determining.
13. The method of claim 11, wherein the at least one address field
includes one or both of a receiver address and a destination
address signalled in the frame header.
14. The method of claim 13, wherein the frame header further
includes a source address field set to an address of the
transmitting station.
15. The method of claim 11, wherein the BSSID uniquely identifying
the second group of stations is a 48-bit MAC address assigned to
the second access point.
16. The method of claim 2, further comprising, at the second access
point: generating a response to the received data, and transmitting
directly the generated response to the transmitting station or
forwarding the generated response to another access point for
transmission to the transmitting station.
17. The method of claim 1, further comprising, at the transmitting
station, receiving a response to the transmitted data, directly
from the second access point or from the second access point via
another access point.
18. The method of claim 16, wherein a frame header of the response
includes a receiver address field set to a basic service set
identification, BSSID, uniquely identifying the group of stations
managed by the other access point, a transmitter address field set
to a BSSID uniquely identifying the second group of stations
managed by the second access point and a destination address field
set to an address of the transmitting station.
19. The method of claim 1, wherein the transmitted data include a
MAC frame embedded in an 802.11ax frame.
20. A wireless communication device forming station in a wireless
network comprising a first access point and a first group of
stations, the first access point managing the first group of
stations, the device forming station in the first group of stations
willing to transmit data to a second access point managing a second
group of stations and comprising at least one microprocessor
configured for carrying out steps of: receiving a trigger frame
from the first access point the trigger frame reserving a
transmission opportunity on at least one communication channel of
the wireless network, the transmission opportunity including
resource units that form the communication channel and that at
least one of the first group of stations can access to transmit
data during the reserved transmission opportunity; and accessing
one of the resource units during the transmission opportunity and
transmitting data intended to the second access point, over the
accessed resource unit to the first access point.
21. A wireless communication device forming a first access point
and a first group of stations, comprising at least one
microprocessor configured for managing the first group of stations,
the microprocessor being further configured for carrying out steps
of: sending a trigger frame to reserve a transmission opportunity
on at least one communication channel of the wireless network, the
transmission opportunity including resource units that form the
communication channel and that at least one of the first group of
stations can access to transmit data during the reserved
transmission opportunity; in response to the trigger frame,
receiving, over one of the resource units during the reserved
transmission opportunity, data from a transmitting station in the
first group of stations and addressed to a second access point
managing a second group of stations; and forwarding the received
data to the second access point.
22. A non-transitory computer-readable storage medium that stores a
program for causing a computer to execute a wireless communication
method in a wireless network comprising a first access point and a
first group of stations, the first access point managing the first
group of stations, the method comprising following steps, at a
transmitting station in the first group of stations willing to
transmit data to a second access point managing a second group of
stations: receiving a trigger frame from the first access point,
the trigger frame reserving a transmission opportunity on at least
one communication channel of the wireless network, the transmission
opportunity including resource units that form the communication
channel and that at least one of the first group of stations can
access to transmit data during the reserved transmission
opportunity; and accessing one of the resource units during the
transmission opportunity and transmitting data intended to the
second access point, over the accessed resource unit to the first
access point.
23. A non-transitory computer-readable storage medium that stores a
program for causing a computer to execute a wireless communication
method in a wireless network comprising a first access point and a
first group of stations, the first access point managing the first
group of stations, the method comprising following steps, at the
first access point: sending a trigger frame to reserve a
transmission opportunity on at least one communication channel of
the wireless network, the transmission opportunity including
resource units that form the communication channel and that at
least one of the first group of stations can access to transmit
data during the reserved transmission opportunity; in response to
the trigger frame, receiving, over one of the resource units during
the reserved transmission opportunity, data from a transmitting
station in the first group of stations and addressed to a second
access point managing a second group of stations; and forwarding
the received data to the second access point.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation of U.S. patent
application Ser. No. 16/610,406, filed on Nov. 1, 2019, which is
the National Phase application of PCT Application No.
PCT/EP2018/060989, filed on Apr. 27, 2018 and titled "MULTI-USER
COMMUNICATION IN A MULTI-BSS ENVIRONMENT OF AN 802.11AX NETWORK".
This application claims the benefit under 35 U.S.C. .sctn.
119(a)-(d) of United Kingdom Patent Application No. 1707062.4,
filed on May 3, 2017. The above cited patent applications are
incorporated herein by reference in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates generally to wireless
communication networks comprising a physical access point (AP) and
stations organized into groups, also known as Basic Service Sets
(BSSs), and more specifically to the transmission of data over a
sub-channel or Resource Unit (RU) forming a transmission
opportunity granted to the AP, and corresponding devices.
[0003] The invention finds application in wireless communication
networks, in particular to the access of an 802.11ax composite
channel and of OFDMA Resource Units forming for instance an
802.11ax channel for Uplink communication towards the AP. One
application of the method regards wireless data communication over
a wireless communication network using Carrier Sense Multiple
Access with Collision Avoidance (CSMA/CA), the network being
accessible by a plurality of station devices.
BACKGROUND OF THE INVENTION
[0004] The IEEE 802.11 MAC family of standards (a/b/g/n/ac/etc.)
defines a way wireless local area networks (WLANs) work at the
physical and medium access control (MAC) level. Typically, the
802.11 MAC (Medium Access Control) operating mode implements the
well-known Distributed Coordination Function (DCF) which relies on
a contention-based mechanism based on the so-called "Carrier Sense
Multiple Access with Collision Avoidance" (CSMA/CA) technique.
[0005] More recently, Institute of Electrical and Electronics
Engineers (IEEE) officially approved the 802.11ax task group, as
the successor of 802.11ac. The primary goal of the 802.11ax task
group consists in seeking for an improvement in data speed to
wireless communicating devices (or stations) used in dense
deployment scenarios.
[0006] In this context, multi-user (MU) transmission has been
considered to allow multiple simultaneous transmissions to/from
different stations (i.e. users) registered with the AP, in both
downlink (DL) and uplink (UL) directions from/to the AP, during a
transmission opportunity granted to the AP over a 20 MHz (or more)
communication channel.
[0007] In the uplink, multi-user transmissions are used to mitigate
the collision probability. This is because multiple non-AP stations
are allowed to transmit simultaneously.
[0008] To actually perform such multi-user transmission, it has
been proposed to split a granted communication channel (or
transmission opportunity granted to the AP) into sub-channels, also
referred to as resource units (RUs), that are usually shared in the
frequency domain between multiple users (non-AP stations/nodes),
based for instance on Orthogonal Frequency Division Multiple Access
(OFDMA) technique.
[0009] Both multi-user Downlink OFDMA and Uplink OFDMA mechanisms
offer overhead reduction as key benefit.
[0010] To perform multi-user (MU) Uplink OFDMA transmission, the AP
sends a control frame, known as Trigger Frame (TF), to the stations
prior they can access one RU of the MU Uplink OFDMA transmission,
either assigned to them or randomly accessible through contention.
RUs are assigned to specific stations in the TF, using the AIDs
associated with the stations upon registration with the AP. Random
RUs are signalled in the TF using an AID set to specific value, and
may be accessed by any station registered with the AP.
[0011] This describes how the stations are managed within a single
BSS handled by the AP with which they have registered.
[0012] In the 802.11 standard, each BSS is uniquely identified
using a specific basic service set identification, BSSID. For a BSS
operating in infrastructure mode, the specific BSSID is usually a
48-bit MAC address of the access point. The specific BSSID is the
formal name of the BSS and is always associated with only one
BSS.
[0013] Together with the specific BSSID, each BSS has its own
service set identification, SSID, which is an informal (human) name
of the BSS (since this own SSID identifier is often entered into
devices manually by a human user).
[0014] Recent developments provide that a single physical AP can
operate as the master stations of a plurality of BSSs, i.e. of a
plurality of independent groups of stations. This avoids using one
physical AP per BSS or WLAN. It also makes it possible to use the
same primary channel for all BSSs, thereby avoiding channel
interference problems. In such a case, it is said that the physical
AP supports Multi-BSSID functionality. For the non-AP stations,
nothing changes.
[0015] When a physical AP supports the multi-BSSID functionality,
the operating scheme is performed through so-called virtual access
points (virtual APs or VAPs) instantiated at the physical AP.
[0016] A Virtual AP is a logical entity that resides within the
physical Access Point (AP) to manage one of the BSSs. Each VAP
appears to the non-AP stations as an independent access point with
its own unique SSID.
[0017] To implement virtual APs, multiple BSSIDs are used with
associated SSIDs. The BSSIDs for the VAPs in the physical AP are
usually generated from a base BSSID specific to the underlying
physical AP, usually the base MAC address of the AP.
[0018] The terms Virtual AP (VAP), specific BSSID, BSS and SSID can
be used synonymously to designate one of the groups or cells of
stations managed by the physical AP.
[0019] Depending on the context, specific BSSID and own SSID may
further refer to the identifier of the corresponding BSS/WLAN,
either through a MAC address (specific BSSID) or an informal
(human) name (own SSID).
[0020] Providing a plurality of SSIDs (or BSSs) corresponds to
providing various different networks in a particular area. It can
give access to different resources and present services which may
have differing management or security policies applied. This
advantageously allows various categories of user, e.g. staff,
students or visitors etc. to be provided with network services
which are appropriate to them.
[0021] In conventional 802.11 approaches, only one SSID (or BSS) is
advertised per signalling message such as a beacon frame. As a
consequence, multiple beacon frames are used to advertise the SSIDs
corresponding to the virtual APs configured at the physical AP.
This solution is compatible with most 802.11 stations and also
allows the SSIDs to support different capability sets.
[0022] However, as the number of BSSs increases, more channel
utilization results from such signalling. This downside is further
increased because the signalling messages are transmitted at low
bit rate, usually at the lowest supported data rate so that all
clients can receive it.
[0023] To improve this situation of increased channel utilization
in case of multiple BSSs, the IEEE 802.11v Wireless Network
Management specification defines a mechanism to advertise network
information (e.g. security profiles including BSSID/SSID and
protection security schemes) of multiple BSSs with a single beacon
frame. This can be made by only one of the VAPs of the physical AP,
namely the "representative" or "transmitted" VAP.
[0024] When a physical AP supports the multi-BSSID functionality,
the handling of MU Uplink OFDMA transmission is made independently
within each BSS as described above: the corresponding VAP sends a
trigger frame identifying the concerned BSS (using the
corresponding BSSID), thereby providing RUs to the stations of the
concerned BSS only.
[0025] Things are slightly different with the representative VAP,
which may assign and thus open access to some RUs triggered by a
sent trigger frame, to stations not belonging to its respective
BSS.
[0026] Recently, the 802.11ax task group has proposed a mechanism
for the AP to reserve one or more RUs of a MU Uplink OFDMA
transmission for not-yet-associated stations (which are 802.11ax
compliant). This is for these stations to speed up their
registration with the AP, by transmitting request management frames
over such reserved RUs (in MU Uplink OFDMA mode). The proposed
mechanism relies on the use of a predefined AID value equal to 2045
to indicate such random RUs the not-yet-associated stations can
access through contention.
[0027] The independence between the BSSs and thus between the
associated granted MU Uplink OFDMA transmissions makes that each
station registered with a specific VAP or willing to register with
it may have to wait for a long and unknown time before a MU Uplink
OFDMA transmission for the appropriate BSS is triggered. This is
particularly unsatisfactory during the association process of
registration with a VAP as the user usually does not want to wait a
long time before being connected. Thus, it is detrimental to user
experience.
[0028] The current operating mode of the 802.11ax multi-user
feature is thus not fully satisfactory, for at least the above
downsides regarding the multi-BSSID functionality.
SUMMARY OF INVENTION
[0029] It is a broad objective of the present invention to improve
this situation, i.e. to overcome some or all of the foregoing
limitations. In particular, the present invention seeks to provide
a more efficient usage of the MU Uplink transmission towards the AP
in the context of multiple BSSs.
[0030] In particular, the Multi-User Uplink communication protocol
is enhanced to allow the stations of a BSS (or willing to join such
BSS) to use RUs provided during the MU Uplink transmission of
another BSS, provided that their communications are forwarding to
the appropriate virtual AP.
[0031] In this context, the present invention proposes enhanced
wireless communication methods in a wireless network comprising a
physical access point and stations organized into groups, the
physical access point implementing a plurality of virtual access
points, each virtual access point managing a group of the stations
and a single one of the virtual access points being a
representative virtual access point authorized to broadcast network
information about a non-representative virtual access point. Such
broadcasting of network information means advertise network
information, e.g. security profiles including BSSID/SSID and/or
protection security schemes, of multiple BSSs with a single control
frame, e.g. a beacon frame.
[0032] In embodiments, the method comprises following steps, at a
transmitting station willing to transmit data to a second virtual
access point managing a second group of stations:
[0033] receiving a trigger frame from a first virtual access point
over the wireless network, the trigger frame identifying a first
group of stations managed by the first virtual access point
different from the second group and reserving a transmission
opportunity on at least one communication channel of the wireless
network, the transmission opportunity including resource units that
form the communication channel and that stations access to transmit
data during the reserved transmission opportunity; and
[0034] accessing one of the resource units not assigned to a
specific station during the transmission opportunity and
transmitting data intended to the second virtual access point, over
the accessed resource unit to the first virtual access point.
[0035] From the AP perspective, enhanced wireless communication
methods are also proposed.
[0036] In embodiments, the method comprises following steps, at the
physical access point:
[0037] sending, by a first virtual access point managing a first
group of stations, a trigger frame identifying the first group of
stations, to reserve a transmission opportunity on at least one
communication channel of the wireless network, the transmission
opportunity including resource units that form the communication
channel and that stations access to transmit data during the
reserved transmission opportunity;
[0038] in response to the trigger frame, receiving, over one of the
resource units during the reserved transmission opportunity, data
from a transmitting station and addressed to a second
(representative or non-representative, but different) virtual
access point managing a second group of stations, different from
the first group identified in the trigger frame; and
[0039] forwarding the received data to the second virtual access
point managing the second group of stations.
[0040] By allowing the first VAP to forward received data not
intended to itself (instead of discarding them) to a second VAP
within the same physical AP, the present invention makes it
possible for the non-AP stations to use RUs provided within a BSS
different from their targeted BSS (with which they are registered
or willing to register).
[0041] Non-AP stations may thus access RUs within MU Uplink
transmissions more often, thereby reducing their waiting time. This
is particularly advantageous to speed up the association process of
registration with a VAP.
[0042] Also, there is provided a wireless communication device
forming station in a wireless network comprising a physical access
point and stations organized into groups, the physical access point
implementing a plurality of virtual access points, each virtual
access point managing a group of the stations and a single one of
the virtual access points being a representative virtual access
point authorized to broadcast network information about a
non-representative virtual access point. The device forming station
willing to transmit data to a second virtual access point managing
a second group of stations and comprises at least one
microprocessor configured for carrying out steps of:
[0043] receiving a trigger frame from a first virtual access point
over the wireless network, the trigger frame identifying a first
group of stations managed by the first virtual access point
different from the second group and reserving a transmission
opportunity on at least one communication channel of the wireless
network, the transmission opportunity including resource units that
form the communication channel and that stations access to transmit
data during the reserved transmission opportunity; and
[0044] accessing one of the resource units not assigned to a
specific station during the transmission opportunity and
transmitting data intended to the second virtual access point, over
the accessed resource unit to the first virtual access point.
[0045] Also, there is provided a wireless communication device
forming physical access point in a wireless network comprising a
physical access point and stations organized into groups. The
device forming physical access point comprises at least one
microprocessor configured for implementing a plurality of virtual
access points, each virtual access point managing a group of the
stations and a single one of the virtual access points being a
representative virtual access point authorized to broadcast network
information about a non-representative virtual access point. The
microprocessor is further configured for carrying out steps of:
[0046] sending, performed by a first virtual access point managing
a first group of stations, a trigger frame identifying the first
group of stations, to reserve a transmission opportunity on at
least one communication channel of the wireless network, the
transmission opportunity including resource units that form the
communication channel and that stations access to transmit data
during the reserved transmission opportunity;
[0047] in response to the trigger frame, receiving, over one of the
resource units during the reserved transmission opportunity, data
from a transmitting station and addressed to a second virtual
access point managing a second group of stations, different from
the first group identified in the trigger frame; and
[0048] forwarding the received data to the second virtual access
point managing the second group of stations.
[0049] Optional features of these embodiments are defined in the
appended claims with reference to methods. Of course, same features
can be transposed into system features dedicated to any device
according to the embodiments of the invention.
[0050] In some embodiments, the first virtual access point is a
non-representative virtual access point.
[0051] In other embodiments, the steps of receiving and forwarding
are performed by the first virtual access point. In that case, the
physical layer of the physical AP may receive the data and transmit
them to the VAP having sent the trigger frame, this VAP being in
charge of performing the appropriate data forwarding. Variants may
contemplate having the physical layer of the physical AP forwarding
(or broadcasting) the received data to each and every VAP
implemented at the physical AP.
[0052] In some embodiments, any station registering with a virtual
access point is associated with a unique association identifier
used by the virtual access point to assign, to the station, a
resource unit in a transmission opportunity granted to the virtual
access point, and
[0053] the resource unit conveying the data of the transmitting
station is assigned to an association identifier not associated
with a specific station.
[0054] It means that a station willing to transmit data to another
BSS (different from the one for which the TF has been sent) may use
RUs having such AID not associated with a specific station. This
makes it possible for the stations to easily identify which RUs can
be used for another BSS.
[0055] In specific embodiments, the association identifier not
associated with a specific station takes a first AID value, for
instance equal to 0, to signal a resource unit in which any station
already registered with any virtual access point implemented by the
physical access point can transmit data. This makes the processing
of the data to be forwarded by the first VAP easier, as they are
concentrated over the RUs with the specific first AID value.
[0056] In some embodiments, the transmitted data include a data
frame intended to the second virtual access point. A data frame is
not dedicated to signalling, e.g. network signalling (such as
management frames of 802.11) and communication signalling (such as
control frames of 802.11).
[0057] In other specific embodiments, the association identifier
not associated with a specific station takes a second AID value,
for instance equal to 2045, to signal a resource unit in which only
a station not yet registered with one of the virtual access points
can transmit data. This makes it possible for the stations to speed
up, with no additional cost, their registration with any VAP, and
not only with the VAP having sent the trigger frame.
[0058] Indeed, the transmitted data may include a management frame
intended to the second virtual access point within a procedure of
associating the transmitting station with the second virtual access
point.
[0059] In some embodiments, the resource unit conveying the data of
the transmitting station is a random resource unit to which
stations randomly access using contention-based access. Indeed,
this makes it possible for any not-designated station to gain
access to the RU, in particular if the station belongs to another
BSS.
[0060] In some embodiments, the data include a frame header in
which at least one address field is set to a basic service set
identification, BSSID, uniquely identifying the second group of
stations (i.e. the second virtual access point). Thanks to this
indication, the first VAP can quickly determine when forwarding
received data (if it is not its own BSSID) and to which VAP of the
same physical AP.
[0061] Indeed, the method may further comprise, at the first
virtual access point, determining whether a frame header of the
received data includes an address field set to the BSSID uniquely
identifying the second group of stations, and forwarding the
received data in case of positive determining.
[0062] According to specific features, the at least one address
field includes one or both of a receiver address and a destination
address signalled in the frame header. This makes the invention
compliant with the conventional MAC frame format. Furthermore, the
frame header may further include a source address field set to an
address of the transmitting station.
[0063] According to another specific feature, the BSSID uniquely
identifying the second group of stations is a 48-bit MAC address
assigned to the second virtual access point.
[0064] In some embodiments, the method at the AP may further
comprise, at the second virtual access point:
[0065] generating a response to the received data, and
[0066] transmitting directly the generated response to the
transmitting station.
[0067] It means the response does not use the same transmission
path as the data (no relay through the first VAP is made). This is
simple to implement with low processing by the physical AP.
[0068] Correspondingly, the method may further comprise, at the
transmitting station, receiving a response to the transmitted data,
directly from the second virtual access point.
[0069] In variants, the method at the AP may further comprise, at
the second virtual access point:
[0070] generating a response to the received data, and
[0071] forwarding the generated response to another (intermediary)
virtual access point implemented at the physical access point for
transmission to the transmitting station.
[0072] Correspondingly, the method may further comprise, at the
transmitting station, receiving a response to the transmitted data,
from the second virtual access point via another virtual access
point implemented at the physical access point.
[0073] For instance, the other virtual access point may be the
first virtual access point or the representative virtual access
point.
[0074] In the first case, the first VAP may advantageously use the
same transmission opportunity, thus reducing overall latency.
Indeed, the VAP may provide both MU Uplink and Downlink OFDMA
transmissions within the same TXOP.
[0075] In the second case, numerous, possibly all, responses can be
concentrated at the representative VAP, which in turn may efficient
use a MU Downlink OFDMA transmission to transmit all the responses
shortly.
[0076] In this case of response path with relay, a frame header of
the response may include a receiver address field set to a basic
service set identification, BSSID, uniquely identifying the group
of stations managed by the other virtual access point, a
transmitter address field set to a BSSID uniquely identifying the
second group of stations managed by the second virtual access point
and a destination address field set to an address of the
transmitting station.
[0077] In some embodiments, the transmitted data include a MAC
frame embedded in an 802.11ax frame.
[0078] Another aspect of the invention relates to a non-transitory
computer-readable medium storing a program which, when executed by
a microprocessor or computer system in a device, causes the device
to perform any method as defined above.
[0079] The non-transitory computer-readable medium may have
features and advantages that are analogous to those set out above
and below in relation to the methods and devices.
[0080] At least parts of the methods according to the invention may
be computer implemented. Accordingly, the present invention may
take the form of an entirely hardware embodiment, an entirely
software embodiment (including firmware, resident software,
micro-code, etc.) or an embodiment combining software and hardware
aspects that may all generally be referred to herein as a
"circuit", "module" or "system". Furthermore, the present invention
may take the form of a computer program product embodied in any
tangible medium of expression having computer usable program code
embodied in the medium.
[0081] Since the present invention can be implemented in software,
the present invention can be embodied as computer readable code for
provision to a programmable apparatus on any suitable carrier
medium. A tangible carrier medium may comprise a storage medium
such as a hard disk drive, a magnetic tape device or a solid state
memory device and the like. A transient carrier medium may include
a signal such as an electrical signal, an electronic signal, an
optical signal, an acoustic signal, a magnetic signal or an
electromagnetic signal, e.g. a microwave or RF signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0082] Further advantages of the present invention will become
apparent to those skilled in the art upon examination of the
drawings and detailed description. Embodiments of the invention
will now be described, by way of example only, and with reference
to the following drawings.
[0083] FIG. 1 illustrates a typical wireless communication system
in which embodiments of the invention may be implemented;
[0084] FIG. 2a illustrates the format of a conventional 802.11 MAC
frame;
[0085] FIG. 2b illustrates an exemplary format of a beacon
frame;
[0086] FIG. 2c illustrates an exemplary format of a Multiple BSSID
element used in beacon frames;
[0087] FIG. 3 illustrates an exemplary sequence of management
frames allowing a not-yet-associated station to discover and
register with a given Access Point;
[0088] FIG. 4 illustrates 802.11ac channel allocation that support
channel bandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz as known in
the art;
[0089] FIG. 5 illustrates an example of 802.11ax MU Uplink OFDMA
transmission scheme, wherein the AP issues a Trigger Frame for
reserving a transmission opportunity of OFDMA sub-channels
(resource units) as known in the art;
[0090] FIG. 6 illustrates a sequence diagram of data exchange
between a non-AP station and a VAP via the MU Uplink OFDMA access
scheme as defined in 802.11ax;
[0091] FIG. 7 shows a schematic representation a communication
device in accordance with embodiments of the present invention;
[0092] FIG. 8 shows a schematic representation of a wireless
communication device in accordance with embodiments of the present
invention;
[0093] FIG. 9 illustrates, using a flowchart, exemplary operations
at a non-AP station according to embodiments of the invention;
[0094] FIG. 10 illustrates, using a flowchart, corresponding
exemplary operations at a virtual AP according to embodiments of
the invention;
[0095] FIG. 11 illustrates a sequence diagram of corresponding data
exchange in 802.11ax from a non-AP station to a physical AP
supporting the Multi-BSSID functionality according to embodiments
of the invention;
[0096] FIG. 12 illustrates, using a flowchart, exemplary operations
at an addressee virtual access point according to embodiments of
the invention;
[0097] FIG. 13 illustrates sequence diagrams of corresponding data
exchange in 802.11ax from the addressee VAP according to various
embodiments of the invention; and
[0098] FIG. 14 illustrates an exemplary sequence of management
frames allowing a station to discover and associate with a virtual
AP according to embodiments of the invention.
DETAILED DESCRIPTION
[0099] The invention will now be described by means of specific
non-limiting exemplary embodiments and by reference to the
figures.
[0100] FIG. 1 illustrates a communication system in which several
communication nodes (or stations) 101-107 exchange data frames over
a radio transmission channel 100 of a wireless local area network
(WLAN), under the management of a central station, or access point
(AP) 110. The radio transmission channel 100 is defined by an
operating frequency band constituted by a single channel or a
plurality of channels forming a composite channel.
[0101] Access to the shared radio medium to send data frames is
based on the CSMA/CA technique, for sensing the carrier and
avoiding collision by separating concurrent transmissions in space
and time.
[0102] Carrier sensing in CSMA/CA is performed by both physical and
virtual mechanisms. Virtual carrier sensing is achieved by
transmitting control frames to reserve the medium prior to
transmission of data frames.
[0103] Next, a source or transmitting station, including the AP,
first attempts through the physical mechanism, to sense a medium
that has been idle for at least one DIFS (standing for DCF
InterFrame Spacing) time period, before transmitting data
frames.
[0104] However, if it is sensed that the shared radio medium is
busy during the DIFS period, the source station continues to wait
until the radio medium becomes idle.
[0105] To access the medium, the station starts a countdown backoff
counter designed to expire after a number of timeslots, chosen
randomly in a contention window range [0, CW], CW (integer) being
also referred to as the Contention Window size and defining the
upper boundary of the backoff selection interval (contention window
range). This backoff mechanism or procedure is the basis of the
collision avoidance mechanism that defers the transmission time for
a random interval, thus reducing the probability of collisions on
the shared channel. After the backoff time period, the source
station may send data or control frames if the medium is idle.
[0106] One problem of wireless data communications is that it is
not possible for the source station to listen while sending, thus
preventing the source station from detecting data corruption due to
channel fading or interference or collision phenomena. A source
station remains unaware of the corruption of the data frames sent
and continues to transmit the frames unnecessarily, thus wasting
access time.
[0107] The Collision Avoidance mechanism of CSMA/CA thus provides
positive acknowledgement (ACK) of the sent data frames by the
receiving station if the frames are received with success, to
notify the source station that no corruption of the sent data
frames occurred.
[0108] The ACK is transmitted at the end of reception of the data
frame, immediately after a period of time called Short InterFrame
Space (SIFS).
[0109] If the source station does not receive the ACK within a
specified ACK timeout or detects the transmission of a different
frame on the channel, it may infer data frame loss. In that case,
it generally reschedules the frame transmission according to the
above-mentioned backoff procedure.
[0110] FIG. 2a illustrates the format of a conventional 802.11 MAC
frame.
[0111] An 802.11 MAC frame contains a MAC header (fields 201 to
207), a Frame Body 208, and a Frame Check Sequence (FCS) 209.
[0112] The MAC header includes the following fields: a Frame
Control field 201 to indicate that the type and subtype of the
frame: data frame, management frame (beacon, authentication,
association frame subtype); a duration field 202; a sequence
control field 206.
[0113] In addition, it may contain up to four address fields: a
first address field 203, referred to as address 1 field, a second
address field 204, referred to as address 2 field, a third address
field 205, referred to as address 3 field and a fourth address
field 207, referred to as address 4 field. The meaning of these
address fields varies from one frame type to the other, and the
content of each one is one from a Source Address (SA) corresponding
to a 48-bit identifier that identifies the source of the current
transmission of the frame, a Destination Address (DA) corresponding
to a 48-bit IEEE MAC identifier that identifies the final recipient
of the frame, a Receiver Address (RA) corresponding to a 48-bit
IEEE MAC identifier that identifies the next immediate recipient of
the frame, a Transmitter Address (TA) corresponding to a 48-bit
IEEE MAC identifier that identifies the wireless interface that
transmitted the frame onto the wireless medium, and a Basic Set
Service Set ID (BSSID) corresponding to a 48-bit identifier that
identifies the Basic Service Set of the VAP considered.
[0114] If the 802.11 MAC frame is a data frame, the content of each
address fields depends on the type of transmission (uplink or
downlink).
[0115] In particular, for an uplink transmission from a non-AP
station to a VAP, the transmitted data frame sets the address
fields as following: address 1 field is set to RA(=BSSID), address
2 field is set to TA (=SA), address 3 is set to DA, and address 4
is not used.
[0116] For a downlink transmission from a VAP to a non-AP station,
the transmitted data frame sets the address fields as following:
address 1 field is set to RA(=DA), address 2 field is set to TA
(=BSSID), address 3 is set to SA, and address 4 is not used.
[0117] This is summarized below:
TABLE-US-00001 Transmission mode Address 1 Address 2 Address 3
Address 4 Uplink: STA to AP RA = BSSID TA = SA DA Not used
Downlink: AP to RA = DA TA = BSSID SA Not used STA
[0118] On the other hand, if the 802.11 MAC frame is a management
frame, the content of each address fields is set as following:
address 1 field is set to DA, address 2 field is set to SA, address
3 is set to BSSID identifying the BSS in which the management
occurs.
TABLE-US-00002 Address 1 Address 2 Address 3 Address 4 DA SA BSSID
Not used
[0119] Back to FIG. 1, in IEEE 802.11 standards, the AP and the
stations registered with it are referred together as a basic
service set (BSS), each BSS being identified by a network
identifier referred to as basic set identifier (BSSID).
[0120] The AP may advertise information about the WLAN
(characteristics of the connection offered to the BSS members)
using management frames, known as beacon frames. Note that a beacon
frame can also be used by stations in an independent BSS (IBSS),
i.e. an ad-hoc network that contains no access point. As an
example, some stations may act as a soft-AP (software implemented),
that is to say implementing all the functionalities of an IEEE
802.11 Access Point but in an ad-hoc or transient connection mode
typically for a specific purpose (e.g. document sharing during a
meeting or multiple-player computer games).
[0121] FIG. 2b illustrates an exemplary format of such a beacon
frame (other formats may exist).
[0122] Illustrated beacon frame 230 l contains 24 bytes of MAC
header (fields 201a to 206a), 0 to 2312 bytes of Frame Body 208a,
and four bytes of Frame Check Sequence (FCS) 209a. The
[0123] MAC header includes the following fields: a frame control
field 201a to indicate that the frame is a management frame of
beacon subtype, a duration field 202a set to zero, a DA field 203a
set to broadcast value FF:FF:FF:FF:FF:FF, a SA field 204a and a
BSSID field 205a.
[0124] The Frame Body is a field of variable length and consists of
two sets of fields: fields that are mandatory 210, followed by
optional fields in the form of Information Elements (IEs) 211.
[0125] Mandatory information in field 210 may contain a Timestamp
representing the time at the access point, which is the number of
microseconds the AP has been active, and allowing synchronization
between non-AP stations in a BSS; Beacon Interval representing the
number of time units (TUs) between successive target beacon
transmission times (TBTTs); and capability Info to indicate
requested or advertised optional capabilities and Supported Rates
fields.
[0126] All Information Elements in field 211 share a common general
format consisting of a 1-byte Element ID field, a 1-byte Length
field, an optional 1-byte Element ID Extension field, and a
variable-length element-specific Information field. Each
information element is identified by the contents of the Element ID
and, when present, Element ID Extension fields as defined in the
802.11 standard. The Length field specifies the number of bytes
following the Length field.
[0127] Back to FIG. 1, since 802.11v, IEEE 802.11 Baseline spec
supports the Multi-BSSID functionality where a single physical AP
implements multiple APs, also known as "virtual APs" or VAP, to
provide multiple local WLANs (or BSSs). In particular, such
Multi-BSSID functionality allows for instance the representative
VAP to send only one beacon frame to advertise network information
about n non-representative virtual AP, instead of having each VAP
sending its own beacon frame (thus n beacon frames on the
medium).
[0128] In FIG. 1, the physical AP 110 supports multiple BSSs and
thus implement two or more VAPs to manage two or more respective
WLANs (or BSSs), i.e. two or more groups of stations. Each BSS has
to be uniquely identified by a specific basic service set
identification, BSSID.
[0129] In the Figure, the physical AP 110 implements two virtual
APs, virtual AP 1 VAP-1 (110A) having MAC address MAC1 as specific
BSSID to manage a first WLAN (BSS) with "guest" as SSID, and
virtual AP 2 VAP-2 (110B) having MAC address MAC2 as specific BSSID
to manage a second WLAN (BSS) with "Employee" as SSID. The security
for each WLAN may be different, i.e. WEP and WPA. Of course more
WLANs can be implemented, requiring a corresponding number of
virtual APs to be implemented in the physical AP.
[0130] Some stations can register with VAP-1 and thus join the
first WLAN "guest", while other stations can simultaneously
register with VAP-2 and thus join the second WLAN
[0131] "Employee".
[0132] An AP device that supports multiple BSSIDs includes two
types of virtual APs. The first one is referred to as "transmitted
AP" or "representative AP". Its BSSID is referred to as transmitted
BSSID. It takes the primary role to transmit Multiple BSSID
elements in beacon and probe response frames. For a given physical
AP, only one virtual AP is designated as transmitted AP.
[0133] The second type of virtual APs is referred to as
"non-representative AP" or "non-transmitted AP". Its BSSID is
referred to as non-transmitted BSSID. The non-representative APs
correspond to other virtual APs which shall not broadcast beacon
frames with Multiple BSSID elements. However they may broadcast
beacon frames specific to their own BSS, i.e. without Multiple
BSSID elements, in order to associate legacy STAs (stations not
implementing IEEE 802.11v) with itself.
[0134] Such beacon frame with multiple BSSID elements may be of the
type shown in FIG. 2b in which the frame body 211 includes one or
more of such BSSID elements to advertise about a plurality of BSSs.
The SA 204a and BSSID 205a fields of the beacon frame are thus sets
to the MAC address of the representative virtual AP transmitting
the beacon frame.
[0135] A Multiple BSSID information element is defined in such
single beacon frame to carry the common, inherited information
element values of all of the BSSIDs and the unique information
elements of the non-representative BSSIDs (non-representative
VAPs). Any station can thus derive the BSSIDs of the
non-representative VAPs from the Multiple BSSID information
element.
[0136] FIG. 2c illustrates an exemplary format of a Multiple BSSID
element.
[0137] The multiple BSSID information element, referenced 211a,
comprises a 1-byte MAX BSSID indicator field 220 and a variable
length Optional Sub-elements field 221. The MAX BSSID Indicator
field is `n`, where 2.sup.n is the maximum number of BSSIDs
supported by the physical access point 110, including the
representative BSSID. Optional Sub-elements field 221 contains zero
or more sub-elements in its Data field, such as for example the
"non-representative BSSID profile" sub-element (each advertising
network information of a non-representative BSS).
[0138] A "non-representative BSSID Profile" is identified by a
Sub-element ID of value 0, and shall include the SSID and multiple
BSSID-index sub-elements for each of the supported BSSIDs. It may
include a Capabilities field followed by a variable number of
information elements.
[0139] The beacon frame may include two or more Multiple BSSID
elements containing elements for a given BSSID index.
[0140] When a station receives a beacon frame with a Multiple BSSID
element that consists of a non-representative BSSID profile with
only the mandatory elements (Capability element, SSID and multiple
BSSID-index), the station may inherit the complete profile from a
previously received beacon frame.
[0141] All MAC addresses identifying the virtual APs are generated
based on (or "derive from") a base MAC address specific to the
physical access point, usually the base 48-bit MAC address of AP
110. For instance MAC.sub.i (`i` being a BSS index) used as
specific BSSID(i) for virtual AP.sub.i is generated as follows,
from the base MAC address BASE_BSSID:
MAC.sub.i=BSSID(i)=(BASE_BSSID modified to set the n LSBs to
zero)|((n LSBs of BASE_BSSID)+i) mod 2^n)
[0142] where LSB refers to the least significant bits, "n" is an AP
parameter (integer) defining the maximum number (about 2.sup.n) of
possible specific BSSIDs, and `|` operator is an XOR operator. The
specific BSSID(i)s thus differ from one another by their n LSBs.
The 48-n MSBs of the generated specific BSSIDs are all similar to
the corresponding bits of BASE_BSSID.
[0143] The same non-AP station can join two WLANs simultaneously
only if it has two separate WLAN interfaces (e.g. wifi network
cards). In that case, the device is considered as two stations in
the network, each station being registered with only one WLAN at a
time.
[0144] For the stations to be aware of available WLANs (or BSSs)
and of the information defining them (for instance corresponding
SSID or SSIDs, corresponding specific BSSID or BSSIDs,
communication mode including Infrastructure or Ad-Hoc, protection
security schemes used including Open, WEP, WPA-PSK or 802.1X,
support transmission rates used, channel in operation, and any
optional Information Elements), the VAPs send some control or
management frames, including beacon frames and probe response
frames which have substantially the same content.
[0145] FIG. 3 illustrates an exemplary sequence of management
frames allowing a not-yet-associated station to discover and
register with a given Access Point. It comprises three phases: WLAN
discovery, authentication and association, at the end of which the
station enters into an authenticated and associated state with the
AP. Note that the station may be currently associated with a first
VAP (i.e. belonging to a first WLAN) and willing to join a second
WLAN.
[0146] 802.11 networks make use of a number of options for the
first phase of 802.11 probing or discovering. For instance, for an
enterprise deployment, the search for a specific network may
involve sending a probe request frame out on multiple channels that
specifies the network name (SSID) and bit rates.
[0147] More generally, prior to association with the VAP, the
stations gather information about the VAPs (or BSSs) by scanning
the channels one by one either through passive scanning or active
scanning.
[0148] In the passive scanning mode, the station scans through
successively each 20 MHz channel and waits to listen for beacon
frames (declaring one or more SSIDs) on the scanned channel,
regardless of whether the stations has already connected to a
specific SSID before or not.
[0149] In the active scanning mode, the stations send out probe
request frames 310 on each wireless 20 MHz channel. The probe
request frames may contain the SSID of a specific WLAN that the
station is looking for or the probe request frames may not contain
a specific SSID meaning the station is looking for "any" SSID in
the vicinity of the station.
[0150] In response to receiving a probe request frame, the VAP
checks whether the station has at least one common supported data
rate or not. If there is a compatible data rate, the VAP responds
with a probe response frame 320, the content of which is similar to
a beacon frame: advertising of the SSID (wireless network name), of
supported data rates, of encryption types if required, and of other
802.11 capabilities of the VAP.
[0151] An acknowledgment frame 330 may be sent by the station, in
response to receiving the probe response frame 320.
[0152] It is also common for a station that is already associated
with a VAP to send probe request frames regularly onto other
wireless channels to maintain an updated list of available WLANs
with best signal strengths. Thanks to this list, when the station
can no longer maintain a strong connection with the VAP, it can
roam to another VAP with a better signal strength using the second
and third phases of the association procedure.
[0153] The second phase is the 802.11 authentication once a WLAN to
join has been chosen by the station. In particular, the station
chooses a compatible WLAN from the probe response frames it
receives.
[0154] 802.11 was originally developed with two authentication
mechanisms: the first authentication mechanism, called "open
authentication", is fundamentally a NULL authentication where the
station says "authenticate me" and the VAP responds with "yes".
This is the mechanism used in almost all 802.11 deployments; the
second authentication mechanism, namely the WEP/WPA/WPA2, is a
shared key mechanism that is widely used in home networks or small
Wi-Fi deployments and provides security.
[0155] During the 802.11 authentication phase, the station sends a
low-level 802.11 authentication request frame 340 to the selected
VAP setting, for instance, the authentication to open and the
sequence to 0x0001. The VAP receives the authentication request
frame 340 and responds to the station with an authentication
response frame 350 set to open indicating a sequence of 0x0002.
[0156] Note that some 802.11 capabilities allow a station to
low-level authenticate to multiple VAPs without being associated
with them (i.e. without belonging to corresponding WLANs). This
speeds up the whole association procedure when the station moves
between VAPs or APs. Indeed, while a station can be 802.11
authenticated to multiple VAPs, it can only be actively associated
and transferring data through a single VAP or AP at a time.
[0157] Next, the station has to perform actual association with the
VAP from the low level authentication step. This is the next phase
of actual 802.11 association by which the station actually joins
the WLAN cell. This stage finalizes the security and bit rate
options and establishes the data link between the station and the
VAP. The purpose of this final exchange is for the station to
obtain an Association Identifier (AID) to be used to access the
medium and send data within the joined WLAN.
[0158] Note that the station may have joined a first network and
may roam from one VAP to another within the physical network. In
that case, the association is called a re-association.
[0159] Once the station determines which VAP (i.e. WLAN) it would
like to be associated with, the station sends an association
request frame 360 to the selected VAP. The association request
frame contains chosen encryption types if required and other
compatible 802.11 capabilities.
[0160] If the elements in the association request frame match the
capabilities of the VAP, the VAP creates an Association ID (AID)
for the station and responds with an association response frame 370
with a success message granting network access to the station. Note
that the AID has to be unique within the same physical AP, meaning
the VAPs share the same range of AIDs.
[0161] Now the station is successfully associated with the VAP,
data transfer can begin in the chosen WLAN using the physical
medium.
[0162] Note that when a VAP receives a data frame from a station
that is authenticated but not yet associated, the VAP responds with
a disassociation frame placing the station into an authenticated
but un-associated state. It results that the station must
re-associate itself with the VAP to join the corresponding
WLAN.
[0163] The probe response frame 320, authentication
request/response frames 340 and 350 and association
request/response frames 360 and 370 are unicast management frames
emitted in an 802.11 legacy format, known as a single user (SU)
format. This is a format used for point-to-point communication
(here between a VAP and the station). Each of these unicast
management frames is acknowledged by an ACK frame 330.
[0164] As indicated above, all the management frames (310, 320,
340, 350, 360, 370) and the ACK frames (330) use the lowest common
rate supported by both the station and the VAP (e.g. 24 mbps or
less).
[0165] To meet the ever-increasing demand for faster wireless
networks to support bandwidth-intensive applications, 802.11ac and
later versions (802.11ax for instance) implement larger bandwidth
transmission through multi-channel operations. FIG. 4 illustrates
an 802.11ac channel allocation that supports composite channel
bandwidth of 20 MHz, 40 MHz, 80 MHz or 160 MHz, by aggregating 20
MHz component channels (400-1 to 400-8).
[0166] A station (including the AP) is granted a transmission
opportunity (TxOP) through the enhanced distributed channel access
(EDCA) mechanism on a 20 MHz channel, referred to as "primary
channel" (400-3) shared by all stations in the same BSS.
[0167] To make sure that no station not belonging to the same BSS
uses the secondary channels, it is provided that the control frames
(e.g. RTS frame/CTS frame or trigger frame described below)
reserving the composite channel are duplicated over each 20 MHz
channel of the 40 MHz, 80 MHz or 160 MHz composite channel.
[0168] Developments in the 802.11ax standard seek to enhance
efficiency and usage of the wireless channel for dense
environments.
[0169] In this perspective, multi-user (MU) transmission features
have been introduced, that allow multiple simultaneous
transmissions to different users in both downlink (DL) and uplink
(UL) directions, once a transmission opportunity has been reserved
and granted to the AP.
[0170] To actually perform such multi-user transmission, a granted
20 MHz channel (400-1 to 400-4) is split into at least one
sub-channel, but preferably into a plurality (usually between two
to nine) of elementary sub-channels, or "sub-carriers" or "resource
units" (RUs) or "traffic channels", that are shared in the
frequency domain by multiple users, based for instance on
Orthogonal Frequency Division Multiple Access (OFDMA)
technique.
[0171] The multi-user feature of OFDMA allows the AP to assign
different RUs to different stations in order to increase
competition within a reserved transmission opportunity TXOP. This
may help to reduce contention and collisions inside 802.11
networks.
[0172] In the MU downlink transmission (from the AP or VAP to the
stations), the AP can directly send multiple data to multiple
stations in the RUs, by simply providing specific indications
within the preamble header of the PPDU sent during the TXOP, and
then sending data in the data field.
[0173] Things are different for the MU Uplink transmissions,
because the AP must control when and how (in which RU) the stations
must emit data.
[0174] Contrary to the MU downlink transmission, a trigger
mechanism has been adopted for the AP to trigger MU uplink
communications from various non-AP stations. This is for the AP to
have such control on the stations (for them to determine the
Resource Units allocation) and to signal medium occupation to
legacy stations (i.e. non-802.11ax stations) for them to set their
NAV.
[0175] As shown in the example of FIG. 5, the AP sends a trigger
frame (TF) 530 to the targeted 802.11ax stations to reserve a
transmission opportunity TXOP 540.
[0176] Based on an AP's decision, the trigger frame TF may define a
plurality of resource units (RUs) 510. The multi-user feature of
OFDMA allows the AP to assign different RUs to different stations
in order to increase competition.
[0177] The trigger frame 530 may define "Scheduled" RUs, which may
be reserved by the AP for certain stations in which case no
contention for accessing such RUs is needed for these stations.
Such scheduled RUs and their corresponding scheduled stations are
indicated in the trigger frame (by associating the AID provided to
the station by the AP with the RU concerned). This explicitly
indicates the station that is allowed to use each Scheduled RU.
Such transmission mode is concurrent to the conventional EDCA
mechanism.
[0178] A non-representative VAP may only assign Scheduled RUs to
stations already registered with it. On the other hand, the
representative VAP may also assign Scheduled RUs to stations
registered with other VAPs (i.e. not belonging to its own BSS)
implemented in the same physical AP.
[0179] The trigger frame TF 530 may also define "Random" RUs, in
addition or in replacement of the "Scheduled" RUs. The Random RUs
can be randomly accessed by stations. In other words, Random RUs
designated or allocated by the AP in the TF may serve as basis for
contention between stations willing to access the communication
medium for sending data. The random RUs are signalled in the TF 530
by associating a specific reserved AID with these RUs. For
instance, an AID equal to 0 is used to identify random RUs
available for contention by stations associated with the AP
emitting the trigger frame (i.e. belonging to the same BSS). On the
other hand, an AID equal to 2045 may be used to identify random RUs
available for contention by stations not yet associated with the
AP
[0180] Note that several random RUs with AID=0 and/or with AID=2045
may be provided by the same TF.
[0181] A random allocation procedure may be considered for 802.11ax
standard based on an additional backoff counter (OFDMA backoff
counter, or OBO counter or RU counter) for random RU contention by
the 802.11ax non-AP stations, i.e. to allow them for performing
contention between them to access and send data over a Random RU.
The RU backoff counter is distinct from the classical EDCA backoff
counters (as defined in 802.11e version). However data transmitted
in an accessed OFDMA RUs 510 is assumed to be served from same EDCA
traffic queues.
[0182] The RU random allocation procedure comprises, for a station
of a plurality of 802.11ax stations having an positive RU backoff
value (initially drawn inside an RU contention window range), a
first step of determining, from a received trigger frame, the
sub-channels or RUs of the communication medium available for
contention (the so-called "random RUs", either identified by a
value 0 for already-associated stations or a value 2045 for
not-yet-associated stations), a second step of verifying if the
value of the RU backoff value local to the considered station is
not greater than the number of detected-as-available random RUs,
and then, in case of successful verification, a third step of
randomly selecting a RU among the detected-as-available RUs to then
send data. In case the second step is not verified, a fourth step
(instead of the third) is performed in order to decrement the RU
backoff counter by the number of detected-as-available random
RUs.
[0183] As one can note, a station having no Scheduled RU is not
guaranteed to perform OFDMA transmission over a random RU for each
TF received. This is because at least the RU backoff counter is
decremented upon each reception of a Trigger Frame by the number of
proposed Random RUs, thereby differing data transmission to a
subsequent trigger frame (depending of the current value of the RU
backoff number and of the number of random RUs offered by each of
further received TFs).
[0184] The stations use the Scheduled and/or Random RUs to transmit
data, in particular MAC data frames during TXOP 540.
[0185] In response to the data transmission, the AP sends a
Multi-User Block Acknowledgment frame 550 to acknowledge the data
received on each RU.
[0186] The MU Uplink (UL) medium access scheme, including both
scheduled RUs and random RUs, proves to be very efficient compared
to conventional EDCA access scheme, especially in dense
environments as envisaged by the 802.11ax standard. This is because
the number of collisions generated by simultaneous medium access
attempts and the overhead due to the medium access are both
reduced.
[0187] Such functioning when the multiple BSS feature is
implemented is explained now with reference to FIG. 6 which
illustrates a sequence diagram of data exchange between a non-AP
station and a VAP via the MU Uplink OFDMA access scheme as defined
in 802.11ax.
[0188] Non-AP station 610 is assumed to be associated with
non-representative VAP 620 (corresponding to the BSSID #2) or is
intended to be associated with it.
[0189] First, the station waits for the reception of a trigger
frame 530 from VAP 620 to transmit data via the MU Uplink OFDMA
access scheme.
[0190] Then, comes the time when VAP 620 sends a trigger frame 650
which is received by non-AP station 610.
[0191] Non-AP station 610 analyses trigger frame 650 to determine
whether or not it can send data (an 802.11 MAC data or management
frame) in a dedicated RU either scheduled (RU identified according
to the AID of station 610) or random (according to the RU random
allocation procedure described above). In case of positive
determining, station 610 builds an 802.11 MAC frame as shown in
FIG. 2a.
[0192] If the 802.11 MAC frame to be constructed is a data frame,
address 1 field (RA/BSSID) is set to the 48-bit IEEE MAC address of
VAP 620, i.e. to BSSID#2; address 2 field (TA/SA) is set to the
48-bit IEEE MAC address of station 610 and address 3 (DA) is set to
the 48-bit IEEE MAC address of the final station to which the data
provided in the payload part 308 are intended.
[0193] If the 802.11 MAC frame to be constructed is a management
frame, address 1 field (DA) is set to the 48-bit IEEE MAC address
of VAP 620, i.e. to BSSID#2, address 2 field (SA) is set to the
48-bit IEEE MAC address of station 610 and address 3 (BSSID) is set
also to the 48-bit IEEE MAC address of VAP 620, i.e. to
BSSID#2.
[0194] Constructed MAC frame 660 is then sent in the dedicated RU
to VAP 620.
[0195] In case of MAC frame 660 is a request from station 610 to
VAP 620, VAP 620 may provide a response by sending a response frame
670 to station 610.
[0196] If response frame 670 is a data frame, address 1 field
(RA/BSSID) is set to the 48-bit IEEE MAC address of VAP 620, i.e.
to BSSID#2; address 2 field (TA/SA) is also set to the 48-bit IEEE
MAC address of VAP 620, i.e. to BSSID#2 and address 3 (DA) is set
to the 48-bit IEEE MAC address of station 610.
[0197] If response frame 670 is a management frame, address 1 field
(DA) is set to the 48-bit IEEE MAC address of station 610, address
2 field (SA) is set to the 48-bit IEEE MAC address of VAP 620, i.e.
to BSSID#2 and address 3 (BSSID) is also set to the 48-bit IEEE MAC
address of VAP 620, i.e. to BSSID#2.
[0198] The process of FIG. 6 happens as soon as a trigger frame
530/650 is received by station 610 from VAP 620. However, the
waiting time before receiving such a trigger frame may be
important, in particular in dense networks where a large number of
VAPs (or BSSs) are implemented by the physical AP. Indeed, the
other VAPs may be granted TXOPs before VAP 620 actually accesses
the medium through conventional EDCA and sends trigger frame
620.
[0199] This waiting time may become detrimental to user experience,
for instance regarding real-time applications (data are sent too
rarely) or regarding the association process by which a user
station may join a WLAN (the users do not accept waiting for a long
time in such process).
[0200] These various drawbacks of the current version of 802.11ax
show that a more efficient usage of the MU Uplink transmission is
sought when the multi BSS feature is enabled.
[0201] The inventors have contemplated allowing the stations to use
specific RUs in MU Uplink transmissions provided by VAPs different
from their own VAP (with which they have registered) to provide
more frequent access to the medium for these stations. An idea of
the inventors to make this approach workable is to configure the
VAP receiving the MU Uplink transmissions (i.e. the VAP having sent
the corresponding trigger frame) to forward data received from a
station belonging to another BSS to the appropriate other VAP.
[0202] A first virtual access point managing a first group of
stations thus sends a trigger frame identifying the first group of
stations, to reserve a transmission opportunity on at least one
communication channel of the wireless network, the transmission
opportunity including resource units that form the communication
channel and that stations access to transmit data during the
reserved transmission opportunity.
[0203] A transmitting station willing to transmit data to a second
virtual access point managing a second (and different) group of
stations thus receives the sent trigger frame, accesses one of the
resource units not assigned to a specific device during the
transmission opportunity and transmits data (e.g. data frame or
management frame) intended to the second virtual access point, over
the accessed resource unit to the first virtual access point.
[0204] In response to the trigger frame, the first virtual access
point thus receives, over one of the resource units during the
reserved transmission opportunity, data from the transmitting
station and addressed to the second virtual access point managing a
second group of stations, different from the first group identified
in the trigger frame; and decides to forward the received data to
the second virtual access point managing the second group of
stations.
[0205] The first virtual access point may thus forward data
received over a Scheduled RU used by a station registered with
another VAP, but also forward data generally received over a Random
RU used by a station registered with another VAP or willing to
register with such other VAP.
[0206] Specific and exemplary implementations of these mechanisms
are described in details below.
[0207] It results that a station, already registered or not with a
VAP, can communicate more frequently with its VAP through MU Uplink
transmissions triggered by any VAP, be it a non-representative or a
representative VAP.
[0208] MU Uplink transmission is thus significantly improved
compared to known current 802.11ax requirements.
[0209] FIG. 7 schematically illustrates a communication device 700,
either a non-AP station 101-107 or the access point 110, of the
radio network 100, configured to implement at least one embodiment
of the present invention. The communication device 700 may
preferably be a device such as a micro-computer, a workstation or a
light portable device. The communication device 700 comprises a
communication bus 713 to which there are preferably connected:
[0210] a central processing unit 711, such as a microprocessor,
denoted CPU; [0211] a read only memory 707, denoted ROM, for
storing computer programs for implementing the invention; [0212] a
random access memory 712, denoted RAM, for storing the executable
code of methods according to embodiments of the invention as well
as the registers adapted to record variables and parameters
necessary for implementing methods according to embodiments of the
invention; and [0213] at least one communication interface 702
connected to the radio communication network 100 over which digital
data packets or frames or control frames are transmitted, for
example a wireless communication network according to the 802.11ax
protocol. The frames are written from a FIFO sending memory in RAM
712 to the network interface for transmission or are read from the
network interface for reception and writing into a FIFO receiving
memory in RAM 712 under the control of a software application
running in the CPU 711.
[0214] Optionally, communication device 700 may also include the
following components: [0215] a data storage means 704 such as a
hard disk, for storing computer programs for implementing methods
according to one or more embodiments of the invention; [0216] a
disk drive 705 for a disk 706, the disk drive being adapted to read
data from the disk 706 or to write data onto said disk; [0217] a
screen 709 for displaying decoded data and/or serving as a
graphical interface with the user, by means of a keyboard 710 or
any other pointing means.
[0218] The communication device 700 may be optionally connected to
various peripherals, such as for example a digital camera 708, each
being connected to an input/output card (not shown) so as to supply
data to the communication device 700.
[0219] Preferably the communication bus provides communication and
interoperability between the various elements included in the
communication device 700 or connected to it. The representation of
the bus is not limiting and in particular the central processing
unit is operable to communicate instructions to any element of the
communication device 700 directly or by means of another element of
the communication device 700.
[0220] The disk 706 may optionally be replaced by any information
medium such as for example a compact disk (CD-ROM), rewritable or
not, a ZIP disk, a USB key or a memory card and, in general terms,
by an information storage means that can be read by a microcomputer
or by a microprocessor, integrated or not into the apparatus,
possibly removable and adapted to store one or more programs whose
execution enables a method according to the invention to be
implemented.
[0221] The executable code may optionally be stored either in read
only memory 707, on the hard disk 704 or on a removable digital
medium such as for example a disk 706 as described previously.
According to an optional variant, the executable code of the
programs can be received by means of the communication network 703,
via the interface 702, in order to be stored in one of the storage
means of the communication device 700, such as the hard disk 704,
before being executed.
[0222] The central processing unit 711 is preferably adapted to
control and direct the execution of the instructions or portions of
software code of the program or programs according to the
invention, which instructions are stored in one of the
aforementioned storage means. On powering up, the program or
programs that are stored in a non-volatile memory, for example on
the hard disk 704 or in the read only memory 707, are transferred
into the random access memory 712, which then contains the
executable code of the program or programs, as well as registers
for storing the variables and parameters necessary for implementing
the invention.
[0223] In a preferred embodiment, the apparatus is a programmable
apparatus which uses software to implement the invention. However,
alternatively, the present invention may be implemented in hardware
(for example, in the form of an Application Specific Integrated
Circuit or ASIC).
[0224] FIG. 8 is a block diagram schematically illustrating the
architecture of the communication device 700, either the AP 110 or
one of stations 101-107, adapted to carry out, at least partially,
the invention. As illustrated, device 700 comprises a physical
(PHY) layer block 803, a MAC layer block 802, and an application
layer block 801.
[0225] The PHY layer block 803 (here an 802.11 standardized PHY
layer) has the task of formatting, modulating on or demodulating
from any 20 MHz channel or the composite channel, and thus sending
or receiving frames over the radio medium used 100, such as 802.11
frames, for instance medium access trigger frames TF 530 (FIG. 5)
to reserve a transmission slot, MAC data and management frames
based on a 20 MHz width to interact with legacy 802.11 stations, as
well as of MAC data frames of OFDMA type having smaller width than
20 MHz legacy (typically 2 or 5 MHz) to/from that radio medium.
[0226] The MAC layer block or controller 802 preferably comprises a
MAC 802.11 layer 804 implementing conventional 802.11ax MAC
operations, and additional blocks 805 and 806 for carrying out, at
least partially, the invention. The MAC layer block 802 may
optionally be implemented in software, which software is loaded
into RAM 712 and executed by CPU 711.
[0227] Preferably, additional block 805, referred to as
multiple-BSS management module for controlling access to random
OFDMA resource units (sub-channels) in case of multiple BSSs,
implements the part of embodiments of the invention that regards
non-AP station and/or VAP operations of device 700.
[0228] Additional block 806, referred as to OFDMA module for
configuring and updating the OFDMA-based MU Uplink random access
procedure, implements the part of embodiments of the invention that
regards non-AP station operations of device 700. The same block 806
may handle the OFDMA-based MU Downlink random access procedure for
the VAPs.
[0229] For instance and not exhaustively, the operations for the
VAP may include generating and sending beacon frames sometimes
identifying a plurality of groups, instead of a single BSS;
generating and sending trigger frames providing RUs for stations of
one or more other BSSs; processing frames received in such RUs to
forward them to appropriate VAPs within the same physical AP;
building and sending responses to requests received from stations;
processing responses to forward them to another VAP in the physical
AP for efficient transmission to requesting stations.
[0230] The operations for a non-AP station may include analyzing
trigger frames received from VAPs to determine if the station is
allowed to access some random RUs in the context of multi-BSS, and
then to actually access such a RU to transmit, during MU Uplink
OFDMA transmission, frames to other VAPs via the VAPs having sent
the trigger frames.
[0231] MAC 802.11 layer 804, multiple-BSS management module 805 and
OFDMA module 806 interact one with the other in order to process
accurately communications over MU Uplink OFDMA RUs provided to
multiple BSSs according to embodiments of the invention.
[0232] On top of the Figure, application layer block 801 runs an
application that generates and receives data packets, for example
data packets of a video stream. Application layer block 801
represents all the stack layers above MAC layer according to ISO
standardization.
[0233] Embodiments of the present invention are now illustrated
using various exemplary embodiments in the context of IEEE 802.11ax
by considering OFDMA RUs dedicated to multiple BSSs.
[0234] Although the proposed examples are also mainly described
with reference to the 802.11ax trigger frames and the management
frames of the 802.11 association process, the present invention is
not limited to such frames.
[0235] FIG. 9 illustrates, using a flowchart, exemplary operations
at a non-AP station according to embodiments of the invention. FIG.
10 illustrates, using a flowchart, corresponding exemplary
operations at a VAP according to embodiments of the invention.
[0236] FIG. 11 illustrates a sequence diagram of corresponding data
exchange in 802.11ax from a non-AP station to a physical AP
supporting the Multi-BSSID functionality according to embodiments
of the invention.
[0237] Non-AP station 1101 (implementing the operations of FIG. 9)
is assumed to be associated or intended to be associated (in which
case its current state is non-associated) with VAP 1103, referred
to as Virtual AP#2, having BSSID #2. Station 1101 is thus willing
to transmit data (e.g. data frame or management frame) to
VAP#2.
[0238] At step 910, a trigger frame 1110 is received from virtual
AP#1 1102 corresponding to BSSID#1 (identified by a TA address
equal to BSSID#1) which is preferably a non-representative VAP (the
representative VAP being virtual AP#0). In the state of the art,
only the non-AP stations associated or intended to be associated
with VAP#1 (having BSSID#1) may participate to the MU Uplink OFDMA
transmission initiated by received trigger frame 1110.
Consequently, stations as in the state of the art (not implementing
the present invention) directly discard trigger frame 1110.
[0239] Note that when a trigger frame is sent by the representative
VAP, the non-AP station does not directly discard the trigger
frame, but checks whether or not one Scheduled RU is assigned to
it, in order to use it, if any.
[0240] On the contrary, with the present invention, station 1101
analyses received trigger frame 1110 at step 920. In particular,
the station checks whether or not the received trigger frame
provides a RU not assigned to a specific station and opened to
stations not related to BSS#1 managed by VAP#1, i.e. whether or not
trigger frame 1110 has assigned one or more dedicated/predefined
RUs to stations not belonging to BSS#1. This is a Random RU in the
meaning that the stations may gain access to it using
contention.
[0241] For instance, such a RU may be identified by a given AID not
associated with a specific station by the VAPs, referred to as
AIDp.
[0242] As an example, AID.sub.p may take a first AID value, for
instance equal to 0, to signal a resource unit in which any station
already registered with any virtual access point implemented by the
physical access point can transmit data.
[0243] As another example, AID.sub.p may take a second AID value,
for instance equal to 2045, to signal a resource unit in which only
a station not yet registered with one of the virtual access points
can transmit data, i.e. stations willing to register with one of
the virtual APs.
[0244] By this mechanism, the invention offers new possibilities to
stations to participate to a MU Uplink transmission initiated
(through a trigger frame) by a first virtual AP, even if the
stations are associated (or intended to be associated) with another
virtual AP.
[0245] Step 920 may optionally check whether the identified RU with
AID=AID.sub.p can be accessed by the station. For instance, the
station may apply the RU random allocation procedure described
above (are there more random RUs with AID=AID.sub.p than an OBO
backoff counter local to the station?) in order to know if it is
allowed to use the RU (to transmit the MAC data) in the current MU
Uplink OFDMA transmission or if it needs to wait for a next
opportunity of medium access.
[0246] In case of positive checking at step 920 (a RU assigned to
an AID equal to AIDp has been identified), next step is step 930;
otherwise the algorithm ends.
[0247] Through steps 930 and 940, the station "catches" the current
MU Uplink OFDMA transmission, although it is not initiated within
its own BSS. Consequently the invention allows an access to the
medium by the stations to be made faster in order to transmit
data.
[0248] At step 930, the station builds the MAC frame to be sent
with appropriate address fields. Various embodiments may be
implemented, each of which provides that the MAC frame includes a
frame header in which at least one address field is set to a basic
service set identification, BSSID, uniquely identifying the second
group of stations, i.e. BSSID#2 in the present example of FIG.
11.
[0249] The embodiments differ from one another in that the at least
one address field having BSSID#2 in the above example includes one
or the other or both of a receiver address and a destination
address signalled in the frame header. Note that the frame header
may further include a source address field set to an address of the
station being about to transmit the data.
[0250] According to first embodiments, only the field usually
corresponding to the BSSID of the BSS in which the MU UL OFDMA
transmission takes place is modified by replacing BSSID#1 (because
the trigger frame has been sent by VAP#1) by BSSID#2.
[0251] In the case of an 802.11 MAC data frame, address 1 field
(RA/BSSID) is set to BSSID#2 (instead of BSSID#1), i.e. to the
48-bit IEEE MAC address of VAP#2 1103, address 2 field (TA/SA) is
set to the 48-bit IEEE MAC address of station 1101 (as done
conventionally) and address 3 (DA) is set to the 48-bit IEEE MAC
address of the final station (as done conventionally).
[0252] In case of an 802.11 MAC management frame (such as frames
310, 340, 360), address 1 field (DA) is set to the 48-bit IEEE MAC
address of the final station (as done conventionally), address 2
field (SA) is set to the 48-bit IEEE MAC address of station 1101
(as done conventionally) and address 3 is set to BSSID#2 (instead
of BSSID#1), i.e. to the 48-bit IEEE MAC address of VAP#2 1103.
[0253] In this way, contrary to the known techniques, a frame with
a BSSID address field (address 1 field for data frame and address 3
field for management frame) equal to a given BSSID (BSSID#2) is
sent during a TXOP initiated by a VAP corresponding to another
BSSID (BSSID#1).
[0254] Second embodiments regard the case where the final station
is the access point itself (which thus not act only as a mere relay
to a final station). In terms of address fields, it means the DA
address field should normally be set to BSSID#1, the VAP initiating
the MU Uplink OFDMA transmission.
[0255] In the second embodiments, only the field corresponding to
the DA is modified by replacing BSSID#1 by BSSID#2.
[0256] In the case of an 802.11 MAC data frame, address 1 field
(RA/BSSID) is set to BSSID#1, i.e. to the 48-bit IEEE MAC address
of VAP#1 1102 having sent the trigger frame (as done
conventionally), address 2 field (TA/SA) is set to the 48-bit IEEE
MAC address of station 1101 (as done conventionally) and address 3
(DA) is set to BSSID#2 (instead of BSSID#1), i.e. to the 48-bit
IEEE MAC address of VAP#2 1103.
[0257] In case of an 802.11 MAC management frame (such as frames
310, 340, 360), address 1 field (DA) is set to BSSID#2 (instead of
BSSID#1), i.e. to the 48-bit IEEE MAC address of VAP#2 1103,
address 2 field (SA) is set to the 48-bit IEEE MAC address of
station 1101 (as done conventionally) and address 3 is set to
BSSID#1, i.e. to the 48-bit IEEE MAC address of VAP#1 1102 having
sent the trigger frame (as done conventionally).
[0258] Third embodiments combine the first and second embodiments.
Thus they also regard the case where the final station is the
access point itself.
[0259] In the third embodiments, both fields corresponding to DA
and to BSSID are modified by replacing BSSID#1 by BSSID#2.
[0260] In the case of an 802.11 MAC data frame, address 1 field
(RA/BSSID) is set to BSSID#2 (instead of BSSID#1), i.e. to the
48-bit IEEE MAC address of VAP#2 1103, address 2 field (TA/SA) is
set to the 48-bit IEEE MAC address of station 1101 (as done
conventionally) and address 3 (DA) is also set to BSSID#2 (instead
of BSSID#1).
[0261] In case of an 802.11 MAC management frame (such as frames
310, 340, 360), address 1 field (DA) is set to BSSID#2 (instead of
BSSID#1), i.e. to the 48-bit IEEE MAC address of VAP#2 1103,
address 2 field (SA) is set to the 48-bit IEEE MAC address of
station 1101 (as done conventionally) and address 3 is also set to
BSSID#2 (instead of BSSID#1).
[0262] Thanks to the indication of BSSID#2 in the MAC frames
received by VAP#1, the latter will be able to decide when
processing by its own the received MAC frames or when forwarding
them to another VAP, as described below.
[0263] Next to step 930, step 940 transmits the built frame 1120
over the dedicated RU determined at step 920.
[0264] Turning now to FIG. 10, VAP#1 receives, at step 1010 and in
response to sent trigger frame 1110 and over one of the resource
units during the reserved transmission opportunity, a MAC frame
from transmitting station 1101. In use, VAP#1 received plenty of
MAC frames over plenty of RUs respectively. For instance, the
physical AP receiving (at its physical layer 803) the MAC frame may
directly transmit the MAC frame to the VAP having transmitted the
trigger frame, i.e. to VAP#1 in the present example.
[0265] The process below is performed for each received MAC
frame.
[0266] At step 1020, VAP#1 determines whether or not the MAC frame
has been received over a RU open to stations not related to BSS#1
managed by VAP#1. In particular, VAP#1 determines whether or not
this RU has an AID equal to an AID not associated with a specific
station, such as AID.sub.p=0 or 2045.
[0267] In case of positive determining, next step is 1030;
otherwise the process goes to step 1040 to process the MAC frame
conventionally.
[0268] As the stations (associated or intended to be associated
with a VAP) may belong to any virtual AP implemented by the
physical AP and not only to VAP #1 (as in the known techniques),
next step 1030 checks whether or not the MAC frame is to be
addressed to a VAP different from VAP#1, for instance to be
addressed to VAP#2 in the above example.
[0269] This may comprise, for VAP#1, to determine whether or not a
frame header of the received MAC frame includes an address field
set to the BSSID uniquely identifying a second group of stations,
i.e. to BSSID#2 in the example. In particular, VAP#1 checks address
1 field and/or address 3 field according to the embodiments
described above.
[0270] In case of positive determining, the MAC frame has to be
addressed to VAP#2. Thus next step is step 1050. Otherwise, the
process goes to step 1040.
[0271] At step 1050, VAP#1 forwards (internally within physical AP
110--reference 1130 in FIG. 11) the received MAC frame to the VAP
corresponding to the BSSID (different from BSSID#1) indicated in
the frame header, i.e. to VAP#2 in the example of FIG. 11. Note
that for the forwarding, the address fields of the MAC frame do not
need to be modified.
[0272] At that time, VAP#2 1103 receives the MAC frame sent by
station 1101, via intermediary VAP#1 1102. It then processes it
accordingly. For instance, if VAP#2 is a gateway to another
(external) network to which a station identified in the DA address
field of the frame header belongs, VAP#2 may merely retransmit the
MAC frame in said other network to the station identified in the DA
address field. In response, VAP#2 may receive other data from this
station to be transmitted to transmitting station 1101.
[0273] Things are quite similar when the MAC frame is a management
frame. In that case, VAP#2 may generate by its own a response to
the received management frame.
[0274] Note that the embodiments described above with reference to
FIGS. 9 to 11 may implement the reception of the MAC frame by the
physical AP and then a transmission of the received MAC frame to
VAP#1 having initially transmitted the trigger frame. Variants may
however be contemplated. For instance, the received MAC frame may
be broadcast, i.e. forwarded, by the physical layer 803 of physical
AP 110 to each and every VAP it implements, and each of these VAPs
is responsible for locally processing the MAC frame. This variant
reduces latency.
[0275] FIG. 12 illustrates, using a flowchart, exemplary operations
at the addressee virtual access point according to embodiments of
the invention. FIG. 13 illustrates sequence diagrams of
corresponding data exchange in 802.11ax from the addressee VAP
according to various embodiments of the invention.
[0276] At step 1210, VAP#2 receives the MAC frame from VAP#1 as
indicated above, said MAC frame having been sent originally by
transmitting non-AP station 1101 identified by address SA in the
frame header of the received MAC frame.
[0277] For instance, the DA address filed of the received MAC frame
corresponds to BSSID#2, meaning that the received MAC frame
corresponds to a request management frame (310, 340, 360) and that
a response is required from VAP#2.
[0278] Next, step 1220 consists for VAP#2 to generate a response
(e.g. 320, 350, 370) to the received MAC frame. The response may
also be the data provided by a station in an external network in
response to the original MAC frame 1120.
[0279] And VAP#2 1103 transmits the MAC frame response to
transmitting station 1101 during step 1230. Various embodiments are
contemplated in which the MAC frame response is transmitted
directly to the transmitting station or forwarded to another
virtual access point implemented at the physical access point for
transmission to the transmitting station, said other virtual access
point being possible VAP#1 1102 (having sent original trigger frame
1110) or the representative virtual access point, noted VAP#0
1104.
[0280] In the case with response forwarding, a frame header of the
response include a receiver address field set to a basic service
set identification, BSSID, uniquely identifying the group of
stations managed by the other virtual access point (forwarding the
response), a transmitter address field set to a BSSID uniquely
identifying the current VAP, VAP#2 in the example, and a
destination address field set to an address of the transmitting
station 1101.
[0281] Direct-transmission embodiments are illustrated in section
(a) of FIG. 13. The MAC frame response 1310 is transmitted directly
to transmitting station 1101 using a Single User EDCA transmission
as known in 802.11.
[0282] In such a case, in the case of an 802.11 MAC data response
frame, address 1 field (RA/BSSID) is set to BSSID#2, address 2
field (TA/SA) is set to BSSID#2 and address 3 (DA) is set to the
48-bit IEEE MAC address of transmitting station 1101.
[0283] In the case of an 802.11 MAC management response frame,
address 1 field (DA) is set to the 48-bit IEEE MAC address of
transmitting station 1101, address 2 field (SA) is set to BSSID#2
and address 3 (BSSID) is also set to BSSID#2.
[0284] In the direct-transmission embodiments, the transmitting
station receives a response to the transmitted data, directly from
the second virtual access point.
[0285] Embodiments with a relay by a non-representative VAP, for
instance VAP#1 1102 having sent the original trigger frame 1110,
are illustrated in section (b) of FIG. 13. The MAC frame response
is forwarded (1320) to VAP#1 1102 for transmission to transmitting
station 1101.
[0286] In such a case, in the case of an 802.11 MAC data response
frame, address 1 field (RA/BSSID) is set to BSSID#1 (instead of
BSSID#2 when VAP#2 wishes to send data to a station), address 2
field (TA/SA) is set to BSSID#2 and address 3 (DA) is set to the
48-bit IEEE MAC address of transmitting station 1101.
[0287] In the case of an 802.11 MAC management response frame,
address 1 field (DA) is set to the 48-bit IEEE MAC address of
transmitting station 1101, address 2 field (SA) is set to BSSID#2
and address 3 is set to BSSID#1 (instead of BSSID#2).
[0288] In such a case, when VAP#1 1102 receives the MAC response
frame, it may use, to relay the MAC response frame 1330 to
transmitting station 1101, the same TXOP that the TXOP used for the
MU Uplink OFDMA transmission having conveyed the MAC request frame
1120. In that way, packet latency is reduced.
[0289] Embodiments with a relay by the representative VAP, namely
VAP#0 1104, are illustrated in section (c) of FIG. 13. The MAC
frame response is forwarded (1340) to VAP#01104 for transmission to
transmitting station 1101.
[0290] In such a case, in the case of an 802.11 MAC data response
frame, address 1 field (RA/BSSID) is set to BSSID#0 (instead of
BSSID#2 when VAP#2 wishes to send data to a station), address 2
field (TA/SA) is set to BSSID#2 and address 3 (DA) is set to the
48-bit IEEE MAC address of transmitting station 1101.
[0291] In the case of an 802.11 MAC management response frame,
address 1 field (DA) is set to the 48-bit IEEE MAC address of
transmitting station 1101, address 2 field (SA) is set to BSSID#2
and address 3 (BSSID) is set to BSSID#0 (instead of BSSID#2).
[0292] In such a case, all the MAC response frames are concentrated
to the representative VAP which in turn may efficient use a MU
Downlink OFDMA transmission to transmit all the responses 1350
together shortly.
[0293] In embodiments with a relay, transmitting station 1101
receives a response to the transmitted data, from VAP#2 via another
VAP implemented at the physical access point.
[0294] The above-described embodiments of the invention may be used
by transmitting station 1101 to perform an association procedure
with VAP#2.
[0295] FIG. 14 illustrates an exemplary sequence of management
frames allowing such a station to discover and associate with VAP#2
according to embodiments of the invention.
[0296] Station 1101 not yet associated with a VAP receives a beacon
frame 1410 from representative VAP#0 1104 (corresponding to the
BSSID#0). The beacon frame 1410 contains the profiles of all VAPs
(including representative and non-representative VAPs) inside
Multiple BSSID elements. In this way, station 1101 is provided with
the list of all available VAPs and BSSs (and their capabilities
which are contained in the non-transmitted profiles). Station 1101
is able to select one of the VAPs without sending a probe request
310.
[0297] In the present example, station 1101 selects VAP#2 1103
(corresponding to BSSID#2).
[0298] Next step of the association process is the transmission of
an authentication request frame 340 by station 1101. To do that,
station 1101 waits for a next opportunity to access the medium,
which is here provided in an MU Uplink OFDMA transmission initiated
by VAP#1.
[0299] Thus, station 1101 receives a trigger frame 1420 from VAP#1
1102 corresponding to the BSSID#1. Using the teachings of the
present invention, station 1101 catches this current MU Uplink
OFDMA transmission by applying above step 910 to 940 to select and
access an RU with AID=2045 to transmit the authentication request
frame 1430.
[0300] VAP#1 1102 receives the authentication request frame and
forward it (1440) to VAP#2 within the physical AP 110, by applying
above steps 1010, 1020, 1030 and 1050.
[0301] VAP#2 thus receives the authentication request frame 1450
and generates (1460) an authentication response frame 1470 by
applying above steps 1210 and 1220. The authentication response
frame 1470 is sent by applying above step 1230.
[0302] As depicted in FIG. 14, the first embodiment with direct
transmission to station 1101 (FIG. 13a) is illustrated.
[0303] Station 1101 thus receives the authentication response frame
1470.
[0304] The next step in the association process is the transmission
of the association request frame 360 by station 1101 to receive an
association response frame 370 from VAP#2. This next step can be
performed in a similar way as described above for the
authentication request frame and the authentication response frame
(references 1420 to 1470).
[0305] Although the present invention has been described
hereinabove with reference to specific embodiments, the present
invention is not limited to the specific embodiments, and
modifications will be apparent to a skilled person in the art which
lie within the scope of the present invention.
[0306] Many further modifications and variations will suggest
themselves to those versed in the art upon making reference to the
foregoing illustrative embodiments, which are given by way of
example only and which are not intended to limit the scope of the
invention, that being determined solely by the appended claims. In
particular the different features from different embodiments may be
interchanged, where appropriate.
[0307] In the claims, the word "comprising" does not exclude other
elements or steps, and the indefinite article "a" or "an" does not
exclude a plurality. The mere fact that different features are
recited in mutually different dependent claims does not indicate
that a combination of these features cannot be advantageously
used.
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